A multitude of female electrical plug receptacles intended for use with 110-125 VAC North American type electrical plugs have been introduced to make an electrical connection with the standard two-pronged or grounded male electrical plug. Particularly where an extension cord is in use, there is a persistent problem in that the plug may inadvertently become disconnected from the receptacle. Such inadvertent disconnection may at best be the cause of decreased productivity, frustration and annoyance, but also can be dangerous, where an unexpected loss of essential power may be the source of potential trouble and perhaps even cause an accident.
The vast majority of male plugs typically include a small 1/8' diameter hole near the end of each prong, usually within a standard range of distance from the plug face. The prior art includes a variety of examples of how these holes may be engaged to prevent inadvertent release. In U.S. Pat. No. 5,286,213 to Altergott et al., small rounded nubs engage the holes in the male prongs. In U.S. Pat. No. 4,319,797 to Otani et al., an electrical connector provides an arm having a hook portion which engages a prong having holes. And, in U.S. Pat. No. 4,932,886 to Glaser, articulated arm assemblies engage the holes of the male prongs.
In spite of these advances, known locking receptacles have not solved the all of the problems of inadvertent disconnection. While some progress has been made at making a secure connection, the prior art has not generally provided structures that will accomplish this task automatically, with safety and economy. As a result, the user is required to twist, press, or in some other manner activate and deactivate the locking mechanism. As a result, such locking structures are not entirely successful at preventing inadvertent disconnection.
Another problem generally seen in the prior art is that some structures employed require a male prong of specific size, shape or design to be compatible. Further, the standard male prongs must be properly aligned for the locking mechanism to function. Some locking mechanisms are poorly adapted to two-prong polarized plugs. Other designs are unforgiving when used with somewhat bent prongs, polarized prongs or excessively worn prongs, and often fail to lock properly.
Another problem seen in the prior art is that the elements forming the locking mechanism are specifically designed for that mechanism only and are not compatible with the standard plug. The twist lock type plugs are typical examples.
Another problem generally seen in the prior art is that the exterior designs do not have a smooth and streamlined body shape that allows the receptacle to flow smoothly along the ground as it is being dragged about. The poor shape design, with its sharp and abrupt edges and corners, allows the body to be caught up in, and snagged by, debris and obstacles, thereby putting unusual strain upon the attached cords and connections inside of both the receptacle and the plug. The resultant stress may lead to frayed insulation, short circuits, loosened terminal connections and other hazards.
Another problem seen in the prior art is that the wiring is inadequately attached to the receptacle. As a result, under repeated strain or momentary shock the wire may come loose from the connector.
A still further problem seen in the prior art is that receptacles fail to provide a cord strain reducing structure that prevents excessive bending and fraying by the cord adjacent to the receptacle. Such a strain reducing structure should be able to accommodate various diameters of commercially available cords.